Geochemical prospecting



Patented Nov. 4, 1941 GEOCHEMICAL PROSPECTING Leo Horvitz, Houston, Tex., assignor to Fsme E. Rosaire, Houston, Tex.

No Drawing. Application November 14, 1939, Serial No. 304,311

Claims.

This invention relates to geochemical exploration for hydrocarbon and associated minerals by soil sample analysis. It relates particularly to a method of utilizing my discovery of carbon monoxide emanations from soil samples. This application is a continuation-in-part of my copending application Serial No. 156,670 filed July 31, 1937, now Patent No. 2,183,964, and entitled Method of exploration of buried deposits.

Experimentation along the lines disclosed in pending application No. 107,497 by E. E. Rosaire and Leo Horvitz has led to the discovery that soil samples heated in the presence of moisture and in a partial vacuum give off a hitherto unsuspected constituent, namely carbon monoxide in measurable amounts. By sampling over a considerable area, it has become evident that the amount of this constituent given off correlates with the location of known hydrocarbon deposits. In fact, small amounts of carbon monoxide have been found in air samples taken above ground, and in air samples taken at the bottom of shallow bore holes.

The exact nature of the reactions involved is not yet known but it is believed that chemical changes in the buried deposits or their emanations produce a complex chemical combination in which carbon monoxide is loosely held in chemical or physical combination such that-it can be liberated. It is also evident that some of this gas is freed by natural processes, since, as above indicated, carbon monoxide is found at the surface of the ground or in shallow bore holes. In any event, in accordance with the present invention the amounts of carbon monoxide are quantitatively determined and experience shows definite correlation between the carbon monoxide anomaly and the presence of hydrocarbon deposits.

Not only have tests been conducted over known oil and gas fields, but fields have been predicted and subsequent drilling has substantiated the predictions.

One object of the invention is to provide means and method for utilizing this newly discovered principle for the purpose of geochemical exploratior'i.

An object is to discover deposits of buried hydrocarbons by sampling soil, and treating the samples in a manner that freed carbon monoxide may be measured quantitatively to determine anomalous conditions which exist by virtue of the presence of buried deposits.

It is also an object of the invention to discover buried carboniferous deposits by taking samples of air, either from bore holes or near the earths surface, and analyzing the air for minute traces of carbon monoxide.

Still another object of the-invention is the discovery of buried deposits of oil,- gas, sulphur, and associated minerals by securing samples of soil or soil gas near the surface of the earth, at a plurality of known points, treating these samples, and measuring the amount of carbon monoxide evolved. J

' Other investigators have made geochemical analyses in the search for buried deposits of oil or gas. Some of these have been indicated by collecting the gas which is often found seeping from points on the earth's surface. If these seeping gases contain ethane or hydrocarbons other than methane, such-a seep isconsidered to be significant in.the search'for burieddeposits of oil or gas. However, the localization of such seeps is materially facilitated by an overlying layer of water, so that seeps are rarely,-if ever, ound upon dry land. Further such seeps may be only marsh gas. 1

I have found that soil at the earths surface which overlies buried hydrocarbon deposits contains carbon monoxide, as well as the previously known carbon dioxide and'hydrocarbon. This gas may be liberated from the soil samples and its amount may be determined by certain treatment of the soil samples. The preferred treatment consists in heating the soil samples in partial vacua. It is noted, however, that-small amounts of gas have been found to be evolved even if the heat treatment is omitted. Analysis of the evolved gases, disclosed the presence of carbon monoxide as well as the previously well known emanations of methane, ethane, carbon dioxide, etc.

Treatment of samples with acid or alkali in addition to heat, moisture, and low pressures has resulted in some cases in an increased carbon monoxide evolution whichincreases the quantitative sensitivity of the method. In a routine method of treatment of samples addition of water to dry samples is deemed advisable.

The cause of the presence of carbon monoxide is not known. It is possible that the presence of this gaseous constituent is the result of partial oxidation of deeply buried deposits, whence the gas migrates in a manner comparable to the migration of hydrocarbon gases as previously known. It is to be understood, however, that this suggested explanation of the presence of this gas is in no way a limitation of the invention, as the invention broadly comprehends a process in which a quantitative determination of this gas reveals anomalies which are correlatable with the presence of buried deposits.

Patches of earth in which carbon monoxide is found are distributed irregularly over the earths surface, and to all outward manifestations do not appear to be different from adjacent, but non-carbon monoxide bearing soil.

In utilizing the present method of geochemical exploration I prefer to secure samples of soil in a more or less uniform spacing over the earth's surface in areas where buried deposits of oil and gas are possible. The samples are preferably taken at a depth exceeding a few feet. Uniform results have been secured by taking the samples at such a depth that they are not affected by climate changes. Samples taken just below the uppermost Water table, generally at a depth of from to 20 feet, have proven satisfactory. Wherever indications of the existence of carbon monoxide concentration are found, the area is explored in greater detail by more-closely spaced analyses.

For reconnaisance surveys where time is of the essence, gas or air sampling may be resorted to, instead of making use of soil samples. While admittedly of lower sensitivity and resolving power, this method has been found to yield useful indications of the presence of the sought deposits. The soil method, of course, is to be preferred since the sample may be subjected to such treatment as found expedient to evolve larger quantities of significant gases than occur naturally.

The method of the present invention may be supplemented by use of other known methods of geophysical exploration; for .example, use of the reflection seismograph may well follow this geochemical survey prior to drilling. Further, this geochemical method of exploration may be used to supplant other indications of the possible existence of a buried deposit of oil, gas, or associated minerals, such as a prospect indicated by the reflection seismograph, magnetometer, or'even a bore hole which'had favorable indications.

Core drilling has furnished an important exploration means, and coring during the drilling of a test well further extends this art. Heretofore, however, cores were used almost exclusively for paleontological and lithological correlation.

' Experimentation has been conducted to find whether carbon monoxide could be evolved from cores. The discovery that carbon monoxide can be evolved and measured, and further that the amount of carbon monoxide correlates with other characteristics such as tectonic structure, character of strata traversed by the borehole, and particularly to proximity to the deposits sought, opens up an entirely new tool for exploration and well logging uses.

Cores may be treated and analyzed for the significant gases without destroying their usefulness to the paleontologists and geologists who may take the cores for further examination after the analysis has been performed. Further, for purposes of well logging it may not even be necessary to core; the cuttings themselves being found to retain enough included carbon monoxide to be useful in the geochemical method herein described. Thus, the same material in the form of cuttings which at present proves valuable in paleontological study may be further examined chemically by the herein disclosed method.

Having fully disclosed my invention, what I desire to claim is:

1. The method of exploration for carboniferous deposits which comprises the steps of taking samples of soil in a region to be explored, treating said sample to evolve in gaseous form constituents extrained therein which are due to leakage from said deposits, and subject the evolved gases to analysis for the quantitative determination therein of carbon monoxide as an indication of proximity of the samples to the sought deposits.

2. The method of exploration for carboniferous deposits by detecting the leakage products from said deposits comprising the step of system atically taking samples of soil air which has diffused upwardly through the substrata from a lower level at selected points in the area to be investigated, and analyzing said air for the quantitative determination of carbon monoxide contained therein.

3. The method of exploration for buried oil,

gas and related deposits comprising taking samples of soil, confining said samples individually. subjecting the samples to heat while confined at a low pressure, to evolve in gaseous form constituents entrained therein which are due to leakage from said deposits, and analyzing said evolved gases for the quantitative determination of carbon monoxide therein as an indication of proximity of the soil samples to the buried deposits.

said deposits, and analyzing said evolved gases for the quantitative determination of carbon monoxide therein as an indication of proximity of the soil samples to the buried deposits.

5. A method according to claim 1 in which the treatment of the samples for the evolution of gases includes a treatment with an acid capable of decomposing carbonates.

LEO HORVITZ. 

